This invention relates to the art of pressurized gas circuit breakers and, more particularly, to an improved method and system for monitoring the pressure of gas in a circuit breaker container and responding to a fault condition relating to the gas pressure.
It is of course well known to provide a circuit breaker in a sealed housing containing an inert gas under pressure which extinguishes the arc which occurs when the breaker opens. It is likewise well known to provide such a circuit breaker with a pressure sensing arrangement and an alarm and/or control circuitry which operates to indicate and/or prevent operation of the circuit breaker in response to a gas leak from the container which results in a pressure drop below a predetermined low pressure level. Such an arrangement is shown, for example, in U.S. Pat. Nos. 3,129,309 to McKeough et al, 3,423,553 to Pratsch and 3,622,725 to McConnell, and the McKeough et al and Pratsch patents further disclose the use of temperature compensated pressure switches for controlling activation of alarm and circuit breaker shutdown devices.
While such pressure sensing arrangements of the foregoing character monitor gas pressure within the circuit breaker container to the extent that they respond to a drop in pressure below a predetermined minimum, they are purely mechanical devices having a set point which has to be mechanically adjusted up or down and which devices rely on a capillary bulb and bellows to provide the temperature compensation controlling switch operation. In addition to being structurally complex and difficult to apply to a breaker and to maintain with respect to the integrity of the temperature compensating capability thereof, all of which lends to an undesirable cost in connection with the construction, installation and maintenance of such systems, it is difficult to obtain and maintain a desired degree of accuracy with respect to the pressure sensing capabilities of such systems. Accordingly, there is a range of inaccuracy with respect to the point of operation of the alarm and/or shutdown control which can lead to a premature and unnecessary actuation of the alarm and/or shutdown control if the pressure in fact is above the acceptable minimum. More importantly, such inaccuracy can result in a dangerous situation if the pressure in the container drops below the acceptable minimum before activation of the alarm and/or shutdown control. Furthermore, the mechanical nature of such arrangements provides for the component parts thereof to be subject to wear and other deterioration which promotes inaccuracy as well as unreliability with respect to the operation thereof.
Moreover, systems of the foregoing character do not provide the capability of detecting a leak until such time as the gas pressure reaches the minimum level and, therefore, do not afford any opportunity to take corrective steps prior to a shutdown condition, or to monitor the leak such as for determining the rate thereof and the time prior to which the pressure will decrease to the minimum level. Accordingly, the monitoring capabilities of such mechanical systems are limited and insufficient and can be costly from the standpoint of downtime and the resulting inconvenience to customers whose power is supplied through the circuit breaker. In this respect, there is no capability of anticipating the point of a shutdown which would enable an intentional shutdown to take place during a time period which would be most convenient with respect to such customers.